Altimeter



July 25, 1950 A. MENZER ETAL- ALTIMETER 5 Sheets-Sheet 1 Filed April 2'7, 1945 aylor elzzer W [LE-N All/FOIL M Filed April 27, 1945 5 Sheets-Sheet 2 20 I INVENTORS Wi l liauLE. Naylor BY A nlbonl Melzzer ATTORNEY July 25, 1950 A. MENZER ETAL ALTIMETER 5 Sheets-Sheet 5 Filed April 27, 1945 INVENTORS William/E.

101' By Ald'on/ Mei/ Z8).

July 25, 1950 A. MENZER r-:r AL 2,516,639

ALTIMETER Filed April 27, 1945 5 Sheets-Sheet 5 Q x. gm ms Williqn z/ E. Naylol' Arr/bola MGILZQIT Patented July 25; 1950 Ridgefield Park; N .12, assignorstd Bendix-reviewtion Corporatiomu Teterboro;. N. .L, ,a corporation of Delaware Application April- 27', 1945; SeriaFNo': 594)}6'64 4'iClaims: 1 a

The present invention relates generally to: barometric pressure instruments and "particularly to sensitive altimeters for aircraft;

An'object of the presentinvention is taprovi'de novelimprovements' in sensitive altimeters for aircraft.

Another object is to provide a" novei'rgeartrain arrangement for" driving a plurality of pointers for use with altimeters and the-like.

Another object is to provide improvementsin instruments embodying a'plurality of scales and pointers for'indicating various altitude ranges; whereby toincr'ease-the altitud'erange of'measurement ofsuch instruments;

Another" object of 'the inventionis toprovide novel improvements in sensitive altimeters to thereby amplify the response of a pressuresensitive means, so'as to=ii1crease the range of the instrument up to 75,000 feet.

Another'object is to provide a novelpointer' gear train adaptedto increase the range ofalti' tude indications and arranged to-beconvertible to thereby provide means for settingthe pointers independently of the pointer actuator.

Another object is to provide novel setting meansfor barometric pressure indicators.

' Anotherobject is to provide ina sensitive altim eter a novel planetary gear'train adaptedto'ih'ave' an increased are of rotation for'barometricset ting.

Still another objectof the invention t0'fp10-' vide novel means in'a sensitive altimeter for set: ting the indicator so as to read'zero at a prede=- termined point of different elevation with respect to the sea; level of a' first point without changingv the" datum of the barometric pressure means in the instrument.

Another object of the present invention isto provide separate directdrives for each pointer shaft of the-instrument to therebye-liminate'drag: onthe fast pointer shaft;

Another objectis" to 1 provide' in an indicating instrument of the class described} improved novel means for setting the instrument for a known; altitude indication at on from a point of destina:-- tion; so that at such'point, the altimeter willshow zero: when the wheelsi of the aircraft touch'itha Y ground:- irrespective of? any" known: variation; in

barometric pressure-anther ground: point of desttination;

Thai above and: other obj ectsiwill appear: more fully hereinafter from thewfollowing detailechdee scription when itakeni in connection with the:ac;-- companying drawings It is-ito=be;ei-ipresslyxunederst0od;,howevergthat the drawingsrarep-for the 2 purposes of 'illustratiomonlit and'iare-notdesigned a'sl-a definition of'ithelimitsiof' the'invention, ref erence beiirg had forthis purpose to -theappended C13;i2I1S- In the drawings; wherein similar reference characters denote: similar? parts throughout the several viewsz Figure; 1 is a top" plan or: front elevation view of i the-indicator dial showing :t'hree hands adapted to" rotate relative thereto;

Figure 2-- a top plan'avi'ew of the instrument with" thedialremove'd showing: thering gear mechanismadapted foi 'diiv iiig the underdial.

Figure'fi isa bottom plan viewrof the instrument removed from thecasingso as-t'o show the relative positions of line-barometric pressure element and its connections;

Figure iis a side elevational view of the barnmetricp'ressure eiement and 'its supporting frame and r0ck-' shaft connections to "the-several mac ca'tor'hand's;

Figure 5' i's a reversedp'erspec-tive ViW of the rock shaft and interconnectedelementswhichare di'iven'from-the barometric pressure-"aneroidi Figure-G' isasid eIevationa-lview of theeritiie instrument showing it* exploded or pulled apart withrespe'ct to=the-casing -which"houses-the oper a-ti'ng parts;-

Figure"' 7 "is-a fragmentary" cross section view of a part of the" instrument casing adapted to show the positioning nieansmounted in the rim thereof for the frame of theinstrument meeh anism Figure 8 isam enlarged 'cross sectional View tal fen along *line 8 8 Of-Fig. 1 of"the indieator hands and the novel' settingmeanstherefor.

Figure 9" isatop-planlongitudinaI View partly broken away of the novel planetary arrangement which makesuptlie setting'mechanism.

Figure 10 is a longitudinal cross sectionai view taken along linezlne -lflv orli igurei-l showing part of the manually controlled setting mechanism, and;

Figure 11" isianenlarged. cross .a sectional view takenalong. line [II-ll ofiI'Figure: 1. showing the connections fromlthe settingknob.

Referring, to the drawings.andffirstj with referenceztoEigures 1 and 6; there-is illustrateda bezel cover. [8 adapted tobe secured. toiaucasing 25 by,- suitablefastemlngvv means i such bolts, or screws l--'! I in correspondingly located.- threaded bores on openings inthe open; end of; casing 25; Readyafor. insertion and; mounting in thecasing 25 is shown the mechanism assembly including an i-aneroidw mountedrin acompound; frame anism therefor, all to be described hereinafter;

in detail;

The casing 25 is provided with a plurality of elongated ribs 25a shown extending longitudinally of the casing terminating in seats 21, in which as 'well as frame [6, may be embedded inwardly extending members, such as pins. 26 to hold'rframe I6 in position. When the entire mechanism carried by the upper frame l6 andthe lower frame 23 is inserted within the casing 25, pins 26 extend through the slots of lugs l9 and center the mechanism in the casing on seats 21 after which a corrugated retaining ring [4 is inserted in-groove l above seats 2? as shown in Figure 8. Referring next to Figures 3, 4 and-5 for further details, the. altimeter may comprise the aneroid carried .by a support or stud'2l which at one end is secured by a split bearing orstud 22 and lock screw 24 carried by the frame 23. Means are provided for transmitting and amplifying the movement of the aneroid 20 upon expansion 0r contraction thereof in response to changes in atmospheric pressure, in order to produce suitable indications of such changes, which indications may be in' terms of barometric pressure or altitude in feet or meters. As shown, such means includes a link 28 pivoted on a bimetal arm 30 in split stud 29, which is secured to the aneroid 20 at one end. Link 28 may be made angular or L-shaped, so as to pivotat the other end on pin 30a in split stud secured to a spring 31, which may be U-shaped as shown, so as to be secured to the head of a bolt" 32 extending from rock shaft 3 l' at substantially right angles to the axis thereof. The rock shaft 3| is journaled between means, such as pivot pin 34 in the end of theintegrally formed bracket 36 of frame 23, and in an eccentrically mounted adjustable hub 33a in plate 38 secured to the lower frame 23 by bolt 39, see Figure 4. Turning of the eccentrically mounted hub 38a, in plate 38 will provide adjustment between sector gear 4! and pinion 42 on pinion shaft 43, which is part of a novelpointer driving gear train hereinafter described. The sector gear 4! is mounted on rock shaft 3! by bushing M and screw 45,se eFigure 5. v

When the aneroid 20 is actuated, the rockshaft 3| will angularly, vary the position of the pinion shaft 43 through its connection with pinion gear 42 by aid of a coil spring anchored to a collar or bushing Ma at its inner coil end and to the bracket 38 at its outer coil end. 'Also, on rock shaft 3! may be mounted the. usual counterweight 41. v

Pointer drive gear train Figure 8 of the'drawings shows the detailed arrangement of the novel pointer driving gear train, which is designed to function as a direct drive to the pointers independently of any plane-' ion shaft 43 journaled in a jewel or other suitable bearing 48 housed within the lower part of the thickness of a large planetary gear 5!, which is the carrier gear of a planetary gear train hereinafter described, and in a smaller jewel or other suitable bearing 53 in lug 55 of the frame 23, so that it is free to rotate when sector gear 4! is turned by deflection of aneroid 20 connected thereto. The large gear 5! is clutched to the frame 23 by a friction spring clutch plate 52, so as to normally remain fixed against rotation in the frame 23.

Mounted on shaft 43 of pinion gear 42 is gear 56, having teeth meshing with a gear 05 having a relatively greater number of teeth than gear 56. The gear is mounted on a shaft 5'! journaled in jewel bearings or other suitable mountings 58 and 59 in eccentric bushings 6| and 32 carried in the apertured bearing arms of parallel upper and lower bearing bracket arms 53 and 54 fixed to gear 5i and extendin in spaced relation above and below the same providing adjustment for setting proper meshing of the gear teeth of the various gears, thus being adjustably mounted in brackets 63 and 64, respectively, secured to the flat upper and lower sides of large planetary gear 5! at an aperture 51a therein b suitable means, such as bolts 53, see Figure 9, so that these parts and gears 55 and 66 turn with the planetary gear'5l.

- Thus it isapparent that shaft 51 is operatively connected or geared to pin-ion shaft 43 by gear 65 in mesh with gear 56, said gear 65 having a relatively greater number of teeth than gear 56, such for example as sixty-five teeth for the gear 65 and sixty-three teeth of gear 56. Gear 65 is free to rotate between bracket 64 and the underside of the normally set large gear 5!. Similarly mounted on the upper end of shaft 57 to also turn with gear 5!, is a gear 66, which in this embodiment to cooperate with the gears 58 and 65 may be provided with sixty-three teeth, and is adapted to rotate with shaft 5! and gear 65. Gear 66 in turn meshes with a gear 61 which may have sixty-five teeth, and is mounted on shaft 68 disposed end to end and above shaft 43, thus providing a differential planetary arrangement for actuating the pointers when large carrier gear 5! is rotated, as to be hereinafter described. The smaller the difference between the relative numbers ofthe intermeshing teeth of gear sets 5665 and EB-6'i, the greater is the arc of planetary movement, and consequently the finer are the possible pointer settings to accord with barometric presure settings up to an altitude of 50,000 feet, or even up to 75,000 feet depending upon the ratio of the number of teeth of the sector gear Al and pinion 42.

The shaft 68 carries above gear 61 the drive gears of the pointer drive arrangement and is rotatably mounted with one end in axial alignment with shaft 43 inthe jewel mounting H, which is seated against the jewel mounting 48 of the pinion shaft 23 and has its other end mounted in a jewel or other suitable bearing 12 seated in a bracket 13 secured to frame 23 below the instrume'nts dial structure hereinafter to be described. The shaft 68 is spring loaded and to prevent back lash by a hair, spring 69 having its inner coil end anchored to the shaft 68 and its outer coil end anchored to a part of bracket 13, and carries alarge gear 15 adapted to connect with the fast pointer shaft 16 through a small pinion H; a relatively smaller but large pinion or gear 18 mounted on or fixed to the shaft 68 above the swam spring 64 m mesh with a gear- 8I-fixed to1thel: sleeve-shaft" 82"of a second speed pointer which is=-mounted concentrically of and turns around shaft -TB; andsmallergean 83 in mesh with a larger gear 84 of a third or slow pointer-"onor.

fiize'd to ahollow or sleeve shaft 85 mounted concentrically of and adapted to turn around the shaft'82'.

The shafts'lt; 82 and 85 are of progressivelyvaried lengths to providefor'receiving and mount=-- ing their respective pointers 86, 81' and88 for" rotation around a suitably marked fixed dial 89* carried bytheframe I6 and having anaperture 9Il -therein to expose a portion of an under-dial: 9 I Shaft 16; for-example, is mounted in a bracket: plate-"I95." andeccentric bushings 80- and 80a in frame 23 so that the mesh between the teeth:

ofpinion TI and gear 15- and? theother sets or pairsof intermeshing gears of the different"-'poi'ntera as described above, may be-a'djusted. The gear ratios of the pointer gear connectionsare= such that the instrument may take care of altitudes up to 55,000 feet or vsgooo feet by varying said'ratios, especially between the sector gear- 4I' For example, gears 11, 8| and and pinion 42; 84- each' are arranged to directly drive their respective pointers 86, 8T and 88', so that the fast pointer BB'indicateS one thousand feet per revolution, thesecond pointer 81 indicates ten thousand movement of gear sector 41, thereby operating poi-nters'86, 8'! and88 in the properratio through" their immediate gear connectiomlE-TI, IS-8|,

and 83-84, driven from the pinion shaft 43 andthrough the gear sets 5E'6 5. and 66-451 carried by normally fixed gear 5 I.

Pointer setting Asis well known in the art'the pointers86, 8-1 and 88 will indicate the altitude with respect to standard barometric pressure at sea-level and notthe true altitude with respect to the ground; 1. e.-, the pointers would indicate zero only when theinstrument is at sea-level under normal conditions. To give true altitude with. respect to any ground altitude, novel means are provided for adjusting the pointersto indicate zero when the instrument is on the ground-regardless of the altitude of theground with respect to. sealevel. Also, such novel means provides'for setting the-instrument for one: condition of ground altitudewith respect to a second condition of al.- titude at some other point: In the: form shown, such novel means'for setting the pointers.com prises a planetary arrangement, which normally constitutes a part of the pointer. geartrain, there being; no planetary actionlexcept when setting the: p int ers.

This planetary arrangement includes the large" carrier gear 55 and the two relativelysma'ller orbitzgears 55 and 66 on the shaft journaled:

in the brackets 03 and 64 secured to the upper and lower sides of planetary gear 5 I;

Large planetary gear 5i is rotable=manually from knob 92 which is secured to shaft 93: re-

siliently'heldidown-by a spring I96 in' an open cavity within a. vertical boss or extension II-51w outsideiof casingzfit see Figures 1.0 and 11 Bee tween bezel-cover I8 'a-ndthe top flange of casing: 25!- and mounted aroundi the: upper end of shaft" 93 is the coil thrust spring: I06 adapted to seat;

in socket I01 in the coverl8- and engage at its other end on flange I08 of shaft 93 so as to retain the-shaftflange lflfi seated against packing I093 An-elengated pinion gear 94-is-fixed to the shaftflil and meshes with the upper gear teeth 98 of a: double gear95: The double gear 95 1s fikedtoa sleeve- 9 5a which is rotatably mounted The sleeve 95dand on" an uprightshaft 96w. gear Stare-urged upwardly by a coil'spring 9'1 abuttihg'thelower'face of'the gear 95 and'thhorizontal'inner wall of the boss 251). A threaded shaft 96 isprovided accessible from thefront I of the instrument" (Fig. 1) which abuts the upper" face--of 'the gear 95 and maintains the teeth 98 and I04 of said gear in mesh with the-gears I0! and IUD- respectively, against the biasof the springs'ri The -gear'1 00 is rotatablymounted on staff I 03 journalledthrough-the frame 23, while the gear" I III" isflxedto the staff I03 and rotates with a gear l02= also'fixed on the staff I03. The gear" I92"'meshes-with'aring gear 99 integral with the" under dial 9i, while the gear I 00 meshes with the large carri'ergear 5| of'the planetary gear train: Rotationofthe knob-92 will thus be trans mitted by; pinion 94'' to the" double gear 95 andthento the gear-99 of the under dial and gear" 5| of the planetary: gear train. By turningthe threaded" staif"96; the pressure thereof wil'lbei release'dffr'om gearttto permit the spring Silto shiftthe'd-oublegear 95so that the'gear teeth" 98*will unmesh fromteeth "II. The rotation of" thek'nobtBZ will now be transmitted only to the" planetary gear" train permitting the indicator hands" to be set withoutfldisturbingthe setting? ofthe under dial :9 I. p

The. gear 51 rotates; in the lower frame 23" against" the resistance or friction" of the spring clutch plate" 52"a'ccording;to the turning of knob 92; and staff 51. mounted'in brackets 63 and .64 carried. byjthe large" planetary gear rotatesiwith itto'thereby provideorbital movementof gears 05- and at with; respect to gears tt'and 67.

staff"?! rotates, differential orbit gears 65 and 65''; move around "gear 56' on. pinion shaft 43" and' gear 6'!" on' shaftGB, and as'pinion shaft 43" is 'heldtfixeddue to" gear sector 4 I being in mesh with pinion-gear 42-fixecl thereto, only shaft 68 andfgearstfiand" 8! are'lmoved. Obviously, movement'ofshaft G'Bwilladjust the pointers 81" and" 88 proportionally through their respectivegears 15 -11; 'IB -BI 33--84, and as pinion shaft 43'" does 'not rotate there" is no interference with" the actuation of-aneroid 20.

With the foregoingarrangement, it is apparentthat thepressureresponsive element 20, whileand-during the timethat-a setting is being made" byrotating'carrier-gear 51 anddiiferential orbit gears fiti and fi fi te-angularly set the pointers, is

constantl'y responsive to barometric pressure for varying altitudes; as it is'undi'sturb'ed' by move=- ment of the planetary geartrain;

The cover I8previously referred'to' has a pair of adja'centapertures in one corner as shown in Figure '13 each of-said apertures being in alignment w-ith drilled'openingsiin the corner of'casing ZBZ-through' whieh extend the knob shaft 93 and" theaslotted end' oflan adjustable shaft- 96 'the exposed upper: endiof which is-slotted for taking: aa. keyz or. screw driverfor adjustment; as shownim Figures: 10 and"; 11, whereby; gears: 98 and IM? maybe adjusted with respect to the intermediate gear I! for the under-dial adjustment and 1 the intermediate gear I00 for providing rotation to large planetary gear 5I,

Operation pressure reported at the groundfor any point v over which, or toward which the airplane is fiy ing, indications of altitude may be corrected while the craft is in flight. I I For example, suppose anairplane takes off from an airport, the elevation of which is precise sea-level. Barometric pressure is exact standard, so the pilot sets the barometric scale I06 on the under-dial to read 29.92 at aperture 90. The air.- port at which the plane plans to land is about 500 miles distant and is also at sea-level elevation.

During flight between the original airport to the distant airport the aneroid will expand upon leaving the earths surface and through linlr 28 motion is transmitted to rock shaft 3|. Gear sector 4| fastened to the rock shaft 3 I, trans-- mits motion through pinion 42 to pinion shaft 43 1 which, in turn, transmits motion to shaft 51. Shaft 51, in turn, transmits motion to shaft 58 through differential gear sets 56--65, 6E6I, and large gear 15 then transmits motion to pinion shaft 16 through pinion 'I! to drive the fast pointer 86. Also, pointers 81 and 88 are likewise driven directly by their respective gearing at relatively slower predetermined speed ratios around the dial 89 to indicate relatively higher altitudes in feet for the original barometric pressure at the starting airport.

However, the objective airport, 500 miles away, has a barometric pressure reading of 29.38 inches of mercury instead of 29.92 inches of mercury and the pilot may-be so informed by radio as he prepares for landing. This lower than standard pressure causes the altimeter to give an altitude indication of 500 feet more than the true altitude, and if the airplane were to land with the barometric scale unchanged, the altimeter would indicate an altitude of 500 feet at the moment the wheels of the craft touched the ground. Under conditions of poor visibility, this could very probably result in a crash landing. However, the pilot upon being duly notified of such prevailing barometric pressure at the ground level of this airport, resets his barometric scale by turning the under-dial 9I to read 29.38, which simultaneously and proportionally turns the interconnected carrier gear 5! of the planetary gear train, so as to set the pointers to indicate altitude based from zero for a barometric reading of 29.38. Conse-- quently, when the wheels of the aircraft touch the ground, the altimeter reads zero.

The actual chain of operation, which causes resetting of the pointers begins with turning knob 92 to simultaneously impart a turn to ring gear 99 of the under-dial 9I and the normally fixed large carrier gear 5I against the frictional resistance of spring clutch plate 52 through double gear 95 and intermediate gears I00 and I02, until a barometric scale reading of 29.38appears through aperture i fin dial 89.

gear sector, 4| actuated only by the aneroid 20 and therefore, gear 56 does not rotate in response to planetation of orbit gear 65, however, shaft 68 is not held against rotation, as it is separatelyjournaled from any driving connection with gear Consequently, such rotation of shaft 58 also turns gears 15,18 and 83 mounted thereon and drives gears 17, 8| and 84 mounted on shafts I6, 82 and a 85, respectively, which gears respectively mesh with each of said gears on shaft 68, to thereby set the respectively associated pointers at proportional speeds to provide indications of true altitudes in feet for the barometric ground presre f=2t38-- Thus there are provided novel improvements in sensitive altimeters, whereby increased ranges of aneroid deflection are obtained by a novel gear 1 train arranged to drive each pointer direct to thereby eliminate drag on the fast pointer shaft and give more sensitivity, and whereby a portion of the novel gear train is convertible to a novel planetary action for setting the indicating point-,

'ers to correct for changes in barometric pressures from one condition for another.

Also, such novel planetary arrangement is so designed that no interference is had with the 1 aneroids position and the instrument will con- ..tinue to give indications of altitude during settings to obtain true altitude readings.

'While only one embodiment of the invention has-been illustrated and described, other changes and modifications which will now appear to those skilled in the art, may be made without departing from the scope of the present invention. Reference is, therefore, to be had to the appended claims for a definition of the limits of the present i invention.

We claim:

1. In an altimeter, means for driving a plurality of indicator hands at different relative speeds comprising an aneroid actuated sector gear, a differential gear train adapted to be driven by said sector gear, a shaft driven by said differential gear train, a plurality of gears of relatively different sizes mountedon said shaft, a first handshaft, a gear on said first hand shaft in mesh with'one of said plurality of gears, a second slower hand shaft around said first hand shaft, a gear on said second slower shaft in mesh with another of said plurality of gears, a third still slower hand shaft mounted around said second hand shaft. a gear on said last-named hand shaft in mesh with :another of said plurality of gears, a hand mounted planetary movement with respect to a desired condition, by thus rotating said differentially driven shaft to a relatively different predeter-. mined angular position representative of said:

desired condition to be attained.

2. A sensitive altimeter including a casing, a

frame in said casing, a plurality of pointer shafts fjournaled for rotation in said frame including a 1 During this periodfiof, setting orbital movement is imparted to gears I55 andq66, which are in mesh with gears 56 and r 61. Pinion shaft 43 is held against rotation by fast pointer shaft, a gear shaft adapted to carry separate gear means for directly driving each of said pointer shafts also journaled for rotation in said frame, intermeshing gear means carried by each of said pointer shafts and said gear shaft, a sector gear, an altitude sensitive means connected to said sector gear adapted to drive the same, a differential gear train in mesh with said gear shaft and adapted to be actuated by said sector gear, and a carrier gear rotatably mounted on said frame to pivot about the axis of rotation of said gear shaft and carrying said differential gear train, means geared to said carrier gear to actuate the same to rotate said differential gear train around the axis of rotation of said gear shaft to thereby provide driving torque to said pointer driving gear shaft and thereby set each of said pointers to function from zero according to any predetermined barometric pressure.

3. In an altimeter, an indicator pointer, means for setting the indicator pointer for predetermined vbarometric pressures prevailing at different locations comprising a rotatable resetting shaft, a double gear rotatable therewith, gear means in mesh with one of said double gears, differential gear means including a friction held gear and a double differential gear rotatably carried thereby arranged for planetary movement around the axis of said carrying gear, said differential gear adapted to normally drive the indicator pointer, a barometric pressure element for rotating said differential gear; the starting cycle of said pointer being adjusted according to a barometric pressure prevailing at another location by the rotation of said carrying gear by the rotation of said resetting shaft providing planetary movement to said differential gear means Without changing the datum of the barometric pressure element, gear means in mesh with the second of said double gears, and means carried by said last gear means and adapted to register with an index for indicating the barometric pressure set into said instrument upon rotation of said resetting shaft.

4. In an altimeter, an indicator pointer, means for setting the indicator pointer for predetermined barometric pressures prevailing at different locations comprising a rotatable resetting shaft, a double gear rotatable therewith and shiftable along its pivotal axis, a spring biasing said double gear in one direction along its pivotal axis, an adjustable abutment in opposed relation to said spring for said double gear, gear means in mesh with one of said double gears, differential gear means including a friction held gear and a double differential gear rotatably carried thereby arranged for planetary movement around the axis of said carrying gear, said differential gear adapted to normally drive the indicator pointer, a barometric pressure element for rotating said differential gear; the starting cycle of said pointer being adjusted according to a barometric pressure prevailing at another location by the rotation of said carrying gear by the rotation of said resetting shaft providing planetary movement to said diiferential gear means without changing the datum of the barometric pressure element, gear means in mesh with the second of said double gears, and means carried by last said gear means and adapted to register with an index for indicating the barometric pressure set into said instrument upon rotation of said resetting shaft, last said gear means being disengageable from said second of said double gears by move-- ment of said adjustable abutment whereby said differential gear means may be adjusted independently of the last said barometric pressure indicating means.

ANTON MENZER. WILLIAM E. NAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,099,467 Carbonara Nov. 16, 1937 2,260,541 Schwenn Oct. 28, 1941 2,325,282 Schwenn July 27, 1943 2,435,289 Raney Feb. 3, 1948 

